Water treatment systems are in widespread use in a variety of applications, and have been provided and proposed in many diverse forms. One application for water handling systems is to collect and treat runoff water that may collect in parking lots, industrial centers, highways, and other places where paved surfaces or other man-made structures inhibit the water's ability to seep into the ground or find its way to natural watercourses. Such runoff water typically is attributable to rainfall, but might come from other natural or man-made sources. It may be suitable, under some circumstances, to simply provide culverts or sewers to collect the runoff water and direct it to a natural watercourse. In many other instances, however, the water will collect and carry debris, sediment, chemicals, or other pollutants that are present along their path, which makes it desirable to treat the water to remove such pollutants before allowing the water to proceed to a natural watercourse. In such cases, a water treatment system may be employed.
One type of conventional water treatment system is a separator tank, which are sometimes called interceptors. These devices typically comprise a container that receives runoff water and forces it to pass under, over or around multiple obstructions that help segregate the water from pollutants. For example, floatable solids and other lighter-than-water pollutants, such as oil and grease, can be separated, to some degree, by forcing the water to pass under an object that skims these substances from the surface of the water. Similarly, sediment and other heavier-than-water substances can be removed by passing the water over obstacles. Of course, the flow rate of the water, turbulence within the separator tank, and many other factors contribute to the ability to separate such pollutants, and it is not necessary to explain such factors in detail here. Examples of known separator tanks are shown in U.S. Pat. Nos. 6,068,765; 6,371,690; 5,753,115; 4,985,148; and 5,498,331, which are all incorporated herein by reference.
One problem associated with all water treatment systems is that the flow rate of the incoming runoff water can fluctuate dramatically, particularly when there are storms or other high-flow events, such as when other runoff paths become obstructed. As a result, engineers specifying the dimensions and capabilities of water treatment systems must anticipate the expected fluctuations, and design the water treatment system accordingly. While it might be possible to simply increase the size of the treatment facility to accommodate any possible influx, doing so might simply be too expensive or the resulting structure might be too large for the given space. Furthermore, the water passing through such an oversized system under higher flow conditions is likely to entrain pollutants that were separated during low flow conditions and carry them downstream. This is sometimes called scouring.
To prevent scouring and provide a more economically sound solution, some treatment systems include a bypass that allows a portion of the storm water to pass through them without being treated. Some of these bypasses, such as those described in the aforementioned patents, are designed to prevent the high flow of storm water from scouring the contents of the treatment tank and carrying the previously-collected pollutants downstream. In these devices, low flows or water are blocked by a weir, which forces the water down through a drop pipe and into a treatment chamber. There, pollutants settle or precipitate out of the water, and then the water ascends out of the tank through a riser pipe to continue downstream. Under high flow conditions, the incoming water exceeds the height of the weir—either because the volume of the water is simply higher than the weir height, or because backpressure in the treatment path causes the water level upstream of the weir to rise above the weir height. Under these conditions, the portion of the water above the weir flows over the weir and to the device's outlet. As it does so, it passes over the drop pipe and also the riser pipe, which can potentially allow some collected contaminants to pass downstream with the storm water.
While the foregoing water treatment systems and other systems have been employed to effectively remove pollutants and prevent scouring, a need still exists for alternative and improved water treatment systems.